Overrunning clutches, such as roller clutches, are used in several automotive applications to allow two rotatable members to rotate in a single selected relative direction. For example, roller clutches may be used instead of sprag clutches as shift timers to improve the smoothness of the vehicle's automatic transmission's shifting. The automatic transmission typically includes a multi-plate fluid operated friction clutch, not to be confused with the overrunning clutch. The friction clutch has a plurality of interleaved friction disks and steel plates. The steel plates are splined to an outer race of the roller clutch while an inner clutch race is journaled on the transmission shaft. The inner race confronts and forms an annular space with the outer race. A cage assembly, which retains a plurality of cylindrical rollers, is installed in the annular space between the races. This location of the roller clutch, radially between the friction clutch and the transmission shaft, saves axial space, but also presents a potential problem. A roller clutch, as opposed to a sprag clutch, has a plurality of circumferentially extending energizing springs, each of which bears on a roller to maintain it in the proper position to be quickly wedged between the races. The disks and plates of the friction clutch, when disengaged, must have a lubricant continually supplied between them to prevent excessive heat and wear. This lubricant is generally supplied from a port in the transmission shaft, and is directed centrifugally outwardly with a force that depends upon the rotational speed. Because the roller clutch cage is, in effect, in the way, that lubricant must go through it. Thus, the energizing springs are liable to be hit by this centrifugally directed lubricant, which may be quite forceful. Of course, the spring is itself subjected to centrifugal forces, as well as to various vibrations and shocks from the vehicle. All of these forces may act to radially dislocate the springs and wear them against the outer race as the roller clutch operates.
A roller clutch energizing spring acts on each roller to continually urge it toward, and maintain it in, what may be termed a ready position. The ready position is a position where the roller is engaged between a respective cam ramp of one race and a cylindrical pathway on the other race, ready to be wedged between the races quickly and automatically, with little or no lost motion, in response to a shift of relative rotation between the two races. In the type of overrunning clutch generally known as a concentricity control clutch, a plurality of evenly circumferentially spaced journal blocks located between the races have rubbing surfaces thereon that slide over the cylindrical pathway as the clutch overruns. The journal blocks have a radial thickness that substantially fills the annular space between the races, thereby maintaining the races in a substantially concentric or coaxial relationship. However, the radial thickness of the journal blocks is deliberately undersized in order that the journal blocks and clutch may be reasonably easily installed between the races. Thus, the races actually rotate relative to each other with a certain degree of running eccentricity, and the radial spacing between the cylindrical pathway and the cam ramps will actually change or oscillate with a very high frequency. That frequency matches or may even be a multiple of engine speed, in the automatic transmission application. The rollers contained between the cam ramps and pathway will consequently roll up and down the cam ramps with the same high frequency, which is referred to as the roller travel. The energizing springs that bear on the rollers must consequently circumferentially expand and contract with the same frequency and over the same path of travel in order to stay with the rollers and maintain them in the ready position. An energizing spring guide means should at least provide radial confinement to prevent the spring from being dislocated and thrown radially into the outer race, which could break the spring. Ideally, such a guide means would do more than that, and would also provide circumferential guidance to the spring as it expands and contracts, without interfering with its travel, and would also prevent it from wearing on the inner race.
Each energizing spring has what may be referred to as an active portion, defined as that portion of the spring that actually flexes as the spring expands and contracts. Thus, the front end of the spring, which directly bears on the roller but does not itself flex, as well as the opposed base of the spring, which is attached to or seats on a mounting portion of the cage, are not active portions of the spring. The most common type of roller clutch energizing spring is what may be referred to as an accordion spring, so named because it is formed of flat spring steel stock bent into a series of flat loops, each adjacent pair of which forms a V. Each loop forms one side of a V, extending between a pair of pleats. As the spring expands and contracts rapidly during operation of the clutch, it is the pleats that are the most highly stressed part of the active portion of the spring, because the majority of spring flexure occurs at and about the pleats. In the most common configuration of accordion energizing spring, the looos extend radially, and the pleats extend axially, within the annular space between the races. Since the loops extend radially, the front dead loop of the spring can be easily stamped with a curvature that conforms to the roller on which it bears. Because of that configuration, however, the highly stressed pleats directly radially confront the metal cam ramps and the cylindrical pathway. It will be well understood how, in an application where the spring is rapidly flexing and is also exposed to the kind of radial dislocating forces described, the crucial spring pleats are potentially highly subject to wear against the races. While the roller-conforming front dead loop of the spring provides some help in keeping the spring from being dislocated radially outwardly, it is not enough to overcome the kinds of forces described above in all applications, and it would be desirable to provide a guides means to prevent that dislocation.
In a less common configuration of accordion spring, the loops extend axially, while the pleats extend radially. Since the loops extend axially, the front dead loop cannot be easily stamped with a curvature that conforms to the roller on which it bears, but is flat, instead. In such a configuration, the pleats confront the side rails of the cage axially, and may rub thereon, but those side rails are often plastic, and are not as likely to wear the pleats as are the metal races. Of course, rubbing contact of the spring pleats with metal cages should be avoided. While it is the edges of the loops that radially confront the metal races, rather than the pleats, it is still desirable to prevent the loops from wearing on the races. And, given the flat front dead loop, there is actually less radial confinement provided to such a spring than with the other configuration, with its roller conforming front end. Furthermore, apart from the wear problem, it is desirable in general that any rubbing contact of the active spring loops with the races or cage, which could tend to interfere with the free flexing of the spring, be avoided. Such contact, even if deliberately provided, could prevent the spring from reacting quickly enough, or prevent it from flexing back and forth along the proper path. Any roller clutch energizing spring guide means that depended upon such deliberate contact would be undesirable for that reason alone. Likewise, any guide means that limited the potential size of the spring and the extent to which the spring could contract and expand, or which limited travel path of the roller, would be undesirable. Limiting the potential radial width of the spring could necessitate using a stiffer, and thus more highly stressed spring material in order to get enough energizing force.
The prior art includes patent disclosures that show various means for confining roller clutch energizing springs, but which say nothing about circumferential spring guidance as such. U.S. Pat. No. 4,368,809 to Husmann discloses an accordion spring of the second type discussed above, one that has radially extending pleats. Husmann provides a flange perpendicular to the front dead loop of the spring that rests against one axial end of the roller, and the spring is deliberately made significantly less wide pleat-to-pleat than the roller length. This serves to keep the pleats spaced away from the side rails of the cage, which is not particularly important unless the cage is metal, but does nothing to keep the spring from being thrown radially into the outer race. U.S. Pat. No. 3,087,588 to Fischer, assigned to the assignee of the present invention, discloses a roller clutch having a metal cage and accordion type energizing springs with pleats that extend axially, rather than radially. Side rails of the cage are interposed radially between the pleats of the spring and the outer race, as best seen in its FIG. 4. In an application subject to the kinds of displacing forces described above, these side rails would prevent the spring from being thrown radially outwardly into the outer race, as may be seen in its FIG. 5. However, that spring confinement would be gained only at the expense of wearing the pleats on the metal side rail, rather than on a metal race, which would be no gain at all. Even with a plastic cage, the clutch in Fischer would be undesirable because of the direct rubbing contact between an active loop of the spring and the cage.
Other references do specifically mention circumferential guidance for the energizing spring, but are still unsuitable. U.S. Pat. No. 4,415,072 to Shoji et al basically concerns a roller clutch in which the rollers are confined relative to the cage structure. However, in FIGS. 9 through 11, it does disclose a purported means for guiding the energizing spring. This means consists of a cross bar extending axially between the side rails of the metal cage. The cross bar is located circumferentially between the base of the energizing spring and the roller, and is located radially between the energizing spring and the outer clutch race. In one embodiment, a cap over the spring would rub back and forth on the underside of the cross bar to guide the spring as the spring expanded and contracted, thereby preventing the spring from being thrown radially into the outer race. In another embodiment, the spring would rub directly on the underside of the cross bar. Such a guide means is undesirable for essentially all the reasons discussed above. The cross bar, located as it is, presents a direct limit on the travel path of the roller. It also limits the potential radial thickness of the spring, and the spring cap would limit the extent of the spring's circumferential expansion and contraction. Without the spring cap, of course, the active loops of the spring would be subjected to deliberate and continual direct wear on the metal cross bar, perhaps several hundred cycles a second, which could be even more detrimental than non-deliberate and intermittent wear on the metal race.
Two foreign references, No. 1,213,177 and No. 1,254,916, (German A.S.) each disclose an apparent energizing spring guide means. Each deliberately does what a spring guide means should avoid, which is to let the spring rub on a metal race. The former shows the spring deliberately rubbing on the outer race, while the latter shows it deliberately rubbing on the inner race. In the '177 reference, the front loop 78 of an accordion spring with radially extending loops has a so called guide member portion 80 bent back integrally therefrom, extending like an umbrella over the outer pleats of the spring and closely confronting a cylindrical portion of the outer race. The guide member 80 is apparently supposed to slide like a shoe along the outer race surface, thereby providing circumferential guidance to the spring as it expands and contracts. Such an arrangement might have some validity if the guide shoe 80 stayed flat to the surface of the outer race on which it was supposed to slide. However, the Vs formed by the adjacent pairs of spring loops, including the front two loops, narrow and widen as the spring contracts and expands, and the guide member 80 would thus be continually changing its angle relative to the surface of the outer race. At the most compressed state of the spring, that angle could be such that the back end of the guide member 80 would jam into a cross bar 32 of the cage, seriously affecting clutch operation. The axially extending juncture between the guide member 80 and the front spring loop 78 from which it was bent would be subjected to continual wear against the outer race, and the guide member 80 would consequently be subject to eventually being disjoined entirely from the spring. Beyond these potential difficulties, the possible radial thickness of the spring would be inevitably limited, as radial room would be occupied by the guide member 80, and nothing at all would prevent the inner spring pleats from rubbing on the inner race. If anything, the guide member, resiliently bouncing of the outer race, would actually throw the inner pleats into the inner race. The '916 reference presents the converse structure. There, a guide member is bent from the front loop back under the lower spring pleats, intended to slide on the inner race. Such a structure would have the same drawbacks as the former structure, and it does nothing to prevent wear of the outer pleats on the outer race, which is the major problem, centrifugal force acting outwardly, not inwardly.